This plate is formed from a slab of stoneware clay and uses the Reuleaux Triangle as the base of the design. The piece is glazed in "safe" glazes which are designed by the maker. It is dishwasher and microwave safe. The scenic decoration is inspired by the high plateau vistas of SE Idaho where we began High Prairie Pottery 50 years ago. Approximately 12 1/2 from point to point. In the case of a Reuleaux Triangle, we could say that was the diameter.